updated 06:45 pm EDT, Mon June 18, 2012

Update available to devs via Mac App Store only

Apple has updated its Mountain Lion Developer Preview 4 for developers, adding new Facebook integration features and the first indications of Power Nap functionality. The original Preview 4 was released at the WWDC a week ago, and today's update isn't the first time Apple has introduced new functionality without offering a new version number. The final release of Mountain Lion is expected sometime next month.

Full Facebook integration in Mountain Lion is not expected to happen in the initial release, with the company's Mountain Lion page promising Facebook "in the fall," or more-or-less in harmony with the expected release of iOS 6, which would explain the delay. Facebook integration between Macs and iOS devices will offer a consistent experience as users shift between devices.

In the new update, Facebook notifications are now integrated into Mountain Lion's Notification Center, including options for friend requests, wall posts, comments, events and other items. Also featured in the update is a setting for Power Nap, a just-announced feature that lets Macs periodically check for email, calendar changes, software updates and other iCloud data even while sleeping.

Machines supported for this build include aluminum 2008 and newer MacBooks, iMacs and MacBook Pros from mid-2007 and newer, the MacBook Air, Mac Pros from 2008 and newer, Mac minis from 2009 and newer, and Xserve machines from 2009, though the list of supported machines may not be final. The sparse releases notes for the update do not mention any progress made on the known issues in DP4.

Any machine running the Developer Preview will not be able to upgrade to the final release without erasing. The update changes the build number to 12A248 (up from 12A239) and is 1.08GB in size. OS X Mountain Lion will sell for $20, one-third less than either Snow Leopard or Lion.